Not applicable.
Not applicable.
The present invention relates to medical nebulizers and in particular to axial piston pumps with noise and operation characteristics suited for use with nebulizers.
Nebulizers are commonly used to deliver medication to persons with respiratory ailments. For example, bronchodialators, which are used to open airway passages, are commonly administered with nebulizers. A nebulizer changes liquid medication into a fine, atomized mist or vapor. The medicinal vapor is inhaled through a mouthpiece or mask and the atomized medication is able to penetrate deeply into one""s airways because of the fine particle size. The liquid medicine is atomized by mixing it with compressed air or oxygen.
Typical nebulizers include a small compressor with a piston that reciprocates rapidly within a cylinder to pressurize the air. U.S. Pat. No. 6,135,144, assigned to the assignee of the present invention and hereby incorporated by reference as though fully set forth herein, discloses a compressor with a wobble piston. The piston is connected by a connecting rod to an eccentric mounted to a rotating shaft so that its head pivots as it slides within the cylinder.
In typical nebulizers, the pressurized air is forced out of the cylinder through a valve head and exhaust chamber to a hose leading to a mixing chamber. Internal conduit is usually necessary to direct the pressurized air leaving the valve head to the outlet port of the housing. After leaving the compressor, the pressurized air passes over an orifice leading from the liquid medicine to aspirate and atomize the medicine, which is then ordinarily mixed with ambient air, oxygen or oxygen enriched air for inhalation.
Persons with significant respiratory problems often require multiple nebulizer treatments every day, each taking several minutes to administer. It is also not uncommon for such persons to receive nebulizer treatments in hospitals, at work or other public places. It is thus important for the nebulizer compressors to operate discreetly. Quiet operation of the compressor can be obtained by insulating the housing, however, this adds bulk and can cause cooling problems. Mufflers can be added at the compressor exhaust, however, this adds hardware and thus cost.
The present invention provides an axial piston pump for use with a nebulizer having improved noise, vibration and manufacturing characteristics.
In one aspect the invention provides a pump with a cylinder and piston disposed along a piston axis and an electromagnet having a stator containing a wire coil driving an armature connected to the piston to reciprocate the piston within the cylinder along the piston axis. The pump has a valve head having an intake port and an exhaust port in communication with the cylinder. The housing defines an exhaust chamber in combination with the valve head that isolates air at the intake port from air at the exhaust port and an outlet extending outside the housing from the exhaust chamber.
In one preferred form, the housing defines a semi-circular exhaust partition and the valve head includes a raised semi-circular wall surrounding the exhaust port and separating it from the intake port. The wall and partition overlap axially in close relation. The valve head wall includes a groove containing an o-ring creating an air tight seal. The valve head can move with respect to the housing and thus a sliding seal is formed between the wall and the partition to seal the exhaust chamber.
The housing also defines an inlet and a baffle spaced from the inlet between the inlet and the intake port to reduce sound and cool the inside of the housing by redirecting intake air before compression.
In another aspect the invention provides a nebulizer pump having a housing with an inlet and an outlet and containing an electromagnet, cylinder, piston valve head and spring system. The spring system includes a plurality of axially spaced leaf springs disposed about and deflectable along the pivot axis and coupled to the piston and the armature of the electromagnet.
Preferably, each leaf spring includes a pair of concentric rings joined by a plurality of spokes and at least one leaf spring is connected to each of the armature and the piston. The springs are clamped in place at each axial side of the electromagnet by two sets of collars or spacer members.
In one form, at least one of the leaf springs is connected to the housing. Alternatively or in addition, the piston and armature can be isolated from the housing by a plurality of coil springs.
The present invention thus provides a compact axial piston pump with low operating vibration and noise such that is particularly suitable for use in a medical nebulizer device. The drive assembly can be suspended in the housing by spring stacks and top and bottom spring mounts to isolate the housing from vibration caused by the reciprocating elements of the assembly, and thereby reduce noise. The springs are selected so that the spring-mass system has a resonant frequency of approximately the input frequency and thereby improves efficiency and reduces vibration and noise. Additionally, the intake air is directed through the housing cavity by inlet baffles formed in the housing to further reduce noise as well as cool the drive assembly components. The unique exhaust chamber construction of the pump, formed by a partition wall of the housing and a mating wall of the valve head, simplifies assembly and cost by eliminating the need for separate exhaust tubing.
These and other advantages of the invention will be apparent from the detailed description and drawings.